One and two-part, curable silicone compositions are well known in the art. One-part systems generally comprise, inter alia, a silicone polymer having hydrolyzable silyl functionality and a catalyst. Upon exposure to a moist atmosphere, the silyl groups react with water to form silanol groups which, in turn, condense to form a cured siloxane network, the condensation being facilitated by the catalyst. However, silicone polymers systems typically cure slowly, i.e., after a few days to a few weeks of exposure to a moist atmosphere.
Prior art solutions to the undesirably slow deep-section cure rate of silicone and hydrocarbon based compositions include the addition of various catalysts and other ingredients as optional components. For example, U.S. Pat. No. 4,435,536 to Kato et al. discloses one-pack, moisture-curable compositions based on hydrolyzable silyl group containing vinyl polymers wherein the inclusion of a solvent imparts storage stability and “workability” to the compositions. When cured, the compositions are said to have excellent surface hardness and weather resistance. The only specific limitation on the solvent is that it does not lead to precipitation when combined with the vinyl polymer and a curing catalyst and it can, therefore, be a hydrocarbon, alcohol, ketone, ether or ester, inter alia. Preferred solvents include alcohols and hydrolyzable esters, methanol, methyl orthoformate, ethyl orthoformate, methyltrimethoxilane and ethyl silicate being specifically illustrated. However, the systems illustrated appear to be cured at elevated temperatures as thin films and are not shown to provide deep-section cure. Additionally, the solvents illustrated either react into the network, or are too volatile to be retained in the composition as it cures. Furthermore, long-chain alkyl alcohols which are also suggested as solvents would tend to undergo an exchange reaction with the hydrolyzable groups on silicon to effectively cap the polymer with a long-chain alkoxy group which is not readily hydrolyzed, thereby interfering with the intended moisture cure.
Importantly, rapid deep-section cure is often desired in certain sealant and/or adhesive applications (e.g., construction, automotive, and insulating glass applications).
As such, there remains a need within the art for rapid deep-cure moisture-curable silicone compositions that overcome this problem.